Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $61.69   10.234%   $68.0034   $68.00   $68.00   $68.00  
  Purchase #2 $99.54   5.143%   $104.6593   $104.66   $104.65   $104.70  
  Purchase #3 $98.94   6.828%   $105.6956   $105.70   $105.70   $105.70  
  Purchase #4 $28.45   6.274%   $30.235   $30.24   $30.25   $30.20  
  Purchase #5 $11.64   5.730%   $12.307   $12.31   $12.30   $12.30  
  Purchase #6 $106.41   6.794%   $113.6395   $113.64   $113.65   $113.60  
  Purchase #7 $117.70   11.580%   $131.3297   $131.33   $131.35   $131.30  
  7 purchase totals = $524.37       $565.8695   $565.88   $565.90   $565.80